Come learn 2000+ kanji and 6000+ vocabulary words with WaniKani.
noun, する verb
If you fall during a cave in you'll fall along with everything around you. And that sinking feeling in your stomach is because... I mean, well you ARE sinking into the ground.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
Why do you think that Toyota fell from being the best in the world?